A typical dehumidifier for a pool enclosure or similar enclosure for a source of humidity incorporates a refrigerant loop with a compressor, a variety of condensers for transferring heat, and an evaporator. The evaporator is used to chill enclosure air to the dew point for extracting moisture. The various condensers are used to heat the pool water or other open receptacle water and reheat the dehumidified enclosure air using the rejection heat. The rejection heat from the refrigerant includes the heat of vaporization of the refrigerant and sensible heat added by the compressor.
The condensers include a desuperheater which is a refrigerant to water heat exchanger (HX) for heating pool water or other open receptacle water such as hot tub, whirlpool bath, spa, shower water etc. Another condenser is the reheat coil, a refrigerant to air HX for reheating the enclosure air using rejection heat. Optional condenser heat exchangers can also be provided for discharging excess sensible heat outside the enclosure. In the case of a refrigerant to air or air cooled condenser for discharging excess heat, the condenser is located outside the enclosure. A refrigerant to water or water cooled condenser for dumping excess heat may be located inside the enclosure. Supplemental heat is added to the enclosure during colder seasons using a separate heating system.
A difficulty with the conventional heat pump system dehumidifiers is that variation in the heating or cooling load for the pool water and enclosure air directly varies the load on the compressor and refrigerant loop. The heat pump system is required to maintain the temperature and humidity of the enclosure air and temperature of the pool water within specified ranges despite variations in pool activity and outside weather conditions. Changes in the load may cause changes in parameters of the refrigerant loop including suction pressure and temperature at the compressor, superheat conditions entering the compressor, and condensing temperature and pressure at the condenser. Operating difficulties occur when changes in load cause refrigeration system parameters to oscillate impairing the efficiency of the heat pump system.